Types of Reaction
- Reactions can be classified as:
- Addition
- Elimination
- Substitution
- Oxidation
- Reduction
- Hydrolysis
- Polymerisation
Addition reactions
- These involve two reactants combining to form one product
- The most common example of an addition reaction involves alkenes, e.g.
C2H4 + H2 → C2H6
C2H4 + Br2 → C2H4Br2
C2H4 + H2O → C2H5OH
Elimination reactions
- These are usually identified by one or two reactants forming more products
- The products often include an alkene and a smaller molecule that has been eliminated from the reactant, e.g.
CH3CH2Br + OH- C2H4 + H2O + Br–
Substitution reactions
- An atom or group of atoms in a compounds is replaced by another atom or group of atoms, e.g.
CH3CH2Br + OH- → C2H5OH + Br–
Oxidation reactions
- This can involve the loss of hydrogen or the gain of oxygen
- A reactant is oxidised by another chemical species, usually an inorganic reagent, e.g.
CH3CHO + [O] → CH3COOH
- In this example, the oxidising agent [O] could be acidified potassium dichromate(VI) solution, Fehling's solution or Tollens' reagent
Reduction reactions
- This can involve the gain of hydrogen or the loss of oxygen
- A reactant is reduced by another chemical species
- This can often be completed using a catalyst and a small reactant molecule such as H2 or HCl, e.g.
CH3CHO + [H] → CH3CH2OH
- In this example, the oxidising agent [H] could be lithium aluminium hydride
Hydrolysis reactions
- The name can be misleading as hydrolysis suggests that water is being used to split (or lyse) a compound
- Hydrolysis reactions are a specific reaction with water, e.g.
CH3Cl + H2O → CH3OH + HCl
Polymerisation reactions
- At AS level, you should know about addition polymerisation
- This is where the carbon-carbon double bond of an alkene monomer breaks open and forms a polymer chain, e.g.
Addition polymerisation of one alkene monomer is polymerised, a (poly)alkene is formed